Methods for thermally processing carbon articles



A Nov. 21, 1961 J. s. ANGEVINE METHODS FOR THERMALLY PROCESSING CARBON ARTICLES 2 Sheets-Sheet 1 Filed April 24, 1957 M w TE NG EN VA m.

ATTORNEY Nov. 21, 1961 J. s. ANGEVINE METHODS FOR THERMALLY PROCESSING CARBON ARTICLES Filed April 24, 1957 2 Sheets-Sheet 2 21:! 2 wmZON OImZON wlmzom mv W.,

me N iO G R WH NA T MN, S A mm m/ UGG @u an oo nm.

3,009,863 METHODS FR THERMALLY PROCESSING CON ARTCLES .lohn S. Angevine, Pittsburgh, Pa., assignor to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 24, 1957, Ser. No. 654,758 13 Claims. (Cl. 202-26) This invention relates generally to the production of shaped carbonaceous products or articles, and is more particularly addressed to a process or method for thermally treating plastically shaped green carbon article-s to convert the same into useable, hard, rigid, baked carbonaceous products, examples of which are electrodes or anodes commonly employed in electrolytic reduction cells or pots for the production of metallic aluminum.

It has been conventional practice to shape or preform green carbon articles by molding, pressing, jolting, tamping or extruding the same from plastic carbon aggregateorganic binder formulations comprising one or more pulverized or comminuted carbon aggregates, such as pitch coke, petroleum coke, bituminous coal coke and anthracite coal, caloined if required, in admixture with an organic binder, such as petroleum pitch or coal-tar pitch, with or without the addition of commercial additives such as lillers and/ or plasticizers,

Thermal treatment of the aforesaid preformed green carbon articles to bake the same has been universally accomplished in batch-type, gas-fired, oil-tired or electrically-heated furnaces in which the plastically shaped green carbon articles lare supported against s-lumping and distortion by surrounding the same with granular packing media, such as coal or coke dust, or by flasks, saggers, or similar boxes of steel or refractory material. The organic b-inder successively softens, melts, loses its lower boiling constituents by devolatilization and is finally converted into coke, with the initially plastic green carbon articles becoming more dense and less readily susceptible to burning during their thermal treatment.

The present invention departs materially from the foresaid prior art practices in that it eliminates the necessity of employment packing media and/or supporting devices in exposed surface area contact with the preshaped green carbon articles and obviates the costly operations associated therewith, including vhandling and ramming the loose granular packing media between and around the preshaped -green carbon products or articles, as well as its removal at the conclusion of a carbon-baking operation, which latter operation normally entails wirebrushing, tumbling, or grit-blasting the baked carbon articles to insure removal of the packing media which adhere to the surfaces of the carbon products during and after baking.

An object of the invention is to provide a method or process of preheating, baking, soaking and cooling plastically formed or shaped green carbon `articles by progressive thermal treatment in the absence of supporting packing media, saggers, asks, and the like, and under substantially inert atmospheric conditions.

Another object of the invention is to provide a thermal treating process for baking plastically formed or shaped green carbon articles by physically moving such articles from one temperature-controlled zone to another to produce uniformly sound, undistorted, rigid, hard, crackfree, baked carbonaceous products or articles, which process provides fo-r the removal and/or disposal of attendant generated distillates and products of carbonization.

Other objects will present themselves to one skilled in the art to which the inveniton pertains on consideration of the following description.

In general, the present invention is directed to thermal processing of preformed green carbon articles, without or in the absence of heretofore employed granular packing media and/or mechanical supporting devices, by progressively moving the green carbon articles through successively arranged preheating, baking, soaking and cooling zones under predetermined temperature conditions in an environment substantially inert to or nonreactive with carbon articles under treatment.

According to the principles of the invention, green carbon articles are plastically preformed or shaped, by molding, tamping, pressing, jolting or extrusion, from carbon aggregate-organic binder Vformulations in which the binder is present in sufficient amount to insure its conversion to coke in the absence of distortion or slumping of the preshaped articles, during the thermal treatments employed in the practice of the invention. In any particular carbon aggregate-binder formulation, the particle-sizing of the aggregate should preferably be selected in such graded sizes as to give a minimum of voids in the finished baked products, and the amount of binder will obviously vary in accordance with the surface area presented bythe carbon particles.

Although the surface area, weight, volume and carbon aggregate-to-binder relationship may be varied within relatively rwide limits when vfabricating the plastically preformed green carbon articles, it is essential to the success of the progressive thermal treatment process of the invention that the carbon aggregate-to-binder relationship be such that the preshaped Kcarbon articles will not only be self-supporting, as initially formed, but will remain so throughout their several successive thermal treatments in the absence of the prior ant granular packing media and/or mechanical surface-contacting supporting devices.

In this connection, it has been discovered that if the preformed `green carbon articles, even 'when prepared as described in the foregoing paragraphs, `are preheated too rapidly, particularly through the plastic temperature range of the binder, the articles will ydeform, crack or slump.

Generally, the greater the quantity of binder, or thicker the coating of binder on the aggregate particles, in the carbon aggregate-binder formulations, the slower the rate of temperature rise that must be employed in the plastic temperature range of the binder.

It has therefore been found that the progressive thermal steps of the invention must of necessity be performed under accurately and closely controlled rates of temperature rise to insure acceptable, sound, baked, carbonaceous articles. In fact, the key to the success of the present invention lies in judicious selection of types and amounts of organic binder, such that the carbon articles will be suiciently plastic to be initially preformed, yet will remain sufliciently rigid when thermally treated in predetermined temperature-controlled, zoned thermal processing, so `as not to distort, slump or crack in an unsupported condition.

Anthracite coal, preferably purified to remove its relatively high ash content, and the purer forms of carbon, such as petroleum coke, the residue from the distillation of petroleum, bituminous coal coke and pitch coke are most generally employed as the carbon aggregatecomponent in the manufacture of baked industrial carbon articles falling within the scope of the invention.

Many types and forms of binders are capable of fulfilling the requirements of the invention, the aromatic organic binders, and mixtures thereof, such as coal-tar pitch, oil-gas pitch, coke-oven pitch, lignite pitch and 3 petroleum pitch, having a cube-in-air melting point between 75 C. and 150 C., and more preferably between 105 C. and 120-C., being preferred. Commercial additives such as llers and/ or plasticizers may also be present in the binders, if desired.

In accordance with the practice of the invention, green carbon products or articles are preformed from mixtures or formulations of the carbon aggregates and the aromatic organic binders by thorough mixing of the components in comminuted form, suicient heat being applied to develop the viscosity and adhesive characteristics of the binders to permit shaping the green carbon articles. Depending on the sizing of the particles of the carbon aggregate, the binder will vary in amount present, smaller amounts of binder being employed with the coarser carbon aggregates.

For example, carbon aggregates Selected from one or more of the group consisting of baked or calcined petroleum coke and pitch coke, Within the following Tyler standard screen analyses- Tyler screen mesh per lineal inch:

Percent aggregate retained on screen in admixture with one or more of the aromatic organic binders selected from the group consisting of petroleum pitch and coal-tar pitch, characterized by a cube-in-air melting point between 75 C. and 150 C., and preferably a cube-in-air melting point between 105 C. and 120 C., the binder being present in amounts between 5 and 25 percent by Weight of the formulations, and preferably in amounts between v12 and 20 percent by Weight, are representative of carbon aggregate-binder formulations responding to the thermal treatment of the invention in the production of acceptable, hard, crack-free and undis- Vtorted baked carbon articles.

Referring now more specilically to the thermal processing steps of the invention, to obviate slumping and distortion of the unpacked and unsupported preshaped green carbon products or articles, it has been found essential to carry out the preheating step under closely and accurately controlled rates of temperature rise up to a predetermined maximum elevated temperature to melt and volatilize substantially all of the lower-boiling constituents of the organic binder through distillation and decomposition of its volatile components and compounds and convert the binder into coke. By means of this preheating step, the green carbon articles are carried through the plastic temperature range of the binder and are transformed into preset, rigid, hard, shaped carbon articles.

Equally important to the success of the invention is the succeeding baking step or operation. Herein the preheated carbon articles are physically advanced or moved, Without intermediate cooling, into a progressively rising and elevated temperature-controlled zone, above the predetermined maximum temperature reached during preheating, where they are elevated to a predetermined maximum baking temperature over a suicient period of time to drive oil substantially all remaining volatile constituents from the green binder coke and carbon aggregate of the preheated carbon articles and crack any remaining gaseous hydrocarbons into coke. This baking step increases the density of the preheated carbon products, Without substantially disturbing their preset condition other than to initiate uniform shrinkage of the same.

The next succeeding step in the progressive thermal treatment method of the invention entails soaking or holding the preheated and baked carbon articles at substantially the maximum predetermined elevated temperature reached during the baking step for a suicient length of time to insure and attain uniform heating throughout the mass of the preheated and baked articles. This soaking step serves to cure the carbon articles by increasing their hardness and density, without introducing shakes, splits and other deleterious properties caused by residual stresses and strains in the carbon articles. The duration of the soaking treatment will depend to some extent upon the degree of devolatilization, cracking and shrinkage obtained in the preheating and baking steps.

The final thermal treatment step, cooling, is preformed by progressively decreasing the temperature of the carbon articles from their predetermined elevated soaking temperature to a predetermined maximum temperature at which the now preheated, baked, soaked and cooled products will not be adversely aiected on their exposure to air. The cooling step is carried out at a rate obviating sudden thermal shock, lwhich depends to some extent, at least, upon the geometric shape and volume of the preformed carbon products.

The four essential thermal steps of the progressive thermal method of the invention above described, to be successful in the absence of protective packing media and/or supporting devices in substantial surface contact with the individual preshaped carbon articles, must be carried out in an environment inert or non-reactive to the carbon articles at all times during their progressive thermal treatment.

From the foregoing desorption, it will be observed that substantial devolatilization of the organic binder and carbon aggregate components of the carbon articles results in the generation of distillation and decomposition by-products. Substantial devolatilization of the binder occurs during the preheating step, which serves to distill off substantially all the lower-boiling constituents and convert substantially all of the binder to coke. Any remaining volatiles are either distilled off or cracked into coke and gaseous carbonization products in the following baking step, where higher-boiling constituents are volatilized.

The natural order and sequence of these devolatilization and coking steps has led to their performance in separately controlled temperature zones to permit removal and/ or disposal of the several resulting by-products in substantial timed relationship with their generation.

For example, the preferred practice of the progressive preheating, baking, soaking and cooling, without intermediate cooling or chilling of the carbon products or articles, in successively disposed temperature-controlled zones, has made it possible to timely and sequentially remove and/or dispose of the lower-boiling fractions of the binder, normally productive of substantial quantities of condensable tar vapors in the preheatin-g zone. Similarly, the higher-boiling devolatilization products of the binder and coke aggregate, which predominately produce sootand/ or coke in the baking and soaking zones, are primarily combustibly consumed in these zones.

The progressive thermal treatment thus far described obviously necessitates the use of apparatus or equipment, and preferred in this respect is a munie-type kiln equipped with controls and facilities capable of providing temperature and atmospheric conditions essential to the practice of the invention. Apparatus found satisfactory in this respect is diagrammatically illustrated in the attached drawings, various details of the equipment well known in the art having been omitted for the sake of clarity and brevity, in which:

FIG. 1 represents a partial sectional plan View of the essential structure of a muletype kiln capable of operation in the performance of the invention;

FIG. 2 represents a medial sectional elevational view of the apparatus of FIG. 1, and

FIG. 3 represents a graph depicting controlled temperature conditions within the kiln of FIGS. 1 and 2.

Generally, the kiln found successful in the practice of the progressive thermal process of the invention comprises an elongated tunnel, ware chamber, or article-receiving compartment or chamber provided with combustion ues along its side walls and intermediate its ends for supplying heat to the same. A lock chamber is provided at the entrance to and eXit from the kiln tunnel to insure against ingress of atmospheric air to the Ware chamber of the kiln.

Control of the desired and required non-reactive or inert gaseous conditions within the interior of the kiln ware chamber is preferably attained through the use of externally supplied gas, although the gases developed within the kiln ware chamber may in whole or in part be employed for this purpose.

More specifically, referring to FIGS. 1, 2 and 3, the kiln apparatus is constructed in the form of an elongated re brick tunnel provided with combustion flues 12 fired by siutable fuel-burning burners 14.

The tunnel 10, along its length from left to right, consists of four zones in direct intercommunication, namely, preheating baking, soaking and cooling zones identied respectively in FIGS. 2 and 3 as zones A, B, C and D. Entrance to zone A and discharge from zone D are accomplished by way of gas lock chambers 1S provided with doors 16 isolating these chambers from the kiln tunnel or ware chamber 10, and doors 18 performing the same function in respect to outside atmosphere. Product-carrying cars 20, or other equivalent well-known conveyor means, traverse the tunnel 10, entrance and eXit to and from the same being intermittent in accordance with the cycle of operation required and dictated by the progressive thermal treatment of the invention.

By Way of example only, and not a limiting factor on the scope of the invention, preshaped 13" X 17 X 12" tall, and larger, plastically formed green carbon anodes fabricated from carbon aggregate-aromatic organic binder formulations of the type described above have been successfully baked in the mufe-type kiln just described under the following controlled thermal conditions.

The preheating step in zone A was carried out to raise the temperature of the preshaped green carbon anodes to between about 400 and 600 C. to devolatilize substantially all of the aromatic organic binder and convert the same into coke. Preheating temperature rises of 2 C. to 40 C. per hour were successfully employed in performing this step of the invention, the actual rate of heating being dictated by the size of the green carbon anodes, their manner of fabrication, and the nature and amount of the binder used.

The preheated carbon anodes were then physically moved, without intermediate cooling below the maximum preheating temperature, into and through zone B, where they were progressively raised in temperature to a predetermined elevated temperature between 800 C. and 1300c C. This step of the invention served to devolatilize or coke substantially all the remaining products of carbonization in the binder and carbon aggregate of the preheated carbon anodes. Since the preheating step servedv to impart an initial set to the green carbon anodes, the rate of temperature rise in the baking zone B is not too critical to the success of the invention. However, a temperature rise of between 4 C. and 50 C. per hour was found satisfactory and practical.

The preheated and baked carbon anodes were next advanced into zone C, where they were held at substantially the maximum predetermined elevated temperature reached during baking for a period of from l to 20 hours. This soaking step served to impart uniform temperature conditions throughout the mass of the carbon anodes, as Well as further densify them and remove any residual strains and stresses therein. Substantially complete devolatilization and carbonization of the binder coke and carbon aggregate of the anodes occurred during the soaking treatment, with accompanying shrinkage of the binder coke and carbon aggregate. The length or duration of the soaking period necessary to impart desired uniformity, shrinkage, and density, in general, increased as the size of the carbon articles or anodes increased, and decreased as the soaking temperature increased.

Following the soaking treatment in zone C, the anodes where physically advanced into and through cooling zone D, where their temperature was progressively lowered to between substantially 200 C. and 400 C., or to a ternperature at which the anodes would not significantly or materially burn or oXidize in air. A cooling rate of between 2 C. and 50 C. per hour was successful in this respect, the actual rate depending mainly on the ability of the kiln equipment to remove heat from the charged carbon products or ware.

It will be observed from the preceding description of the invention that two distinct sets of operating conditions must be properly utilized and correlated while the carbon articles are moving through the kiln tunnel 10. First, heat must be supplied in controlled amounts, distributed, a'nd imparted to the carbon articles in an accurately controlled manner throughout the preheating, baking and soaking zones of the kiln. Secondly, the by-products of the progressive thermal treatment aforedescribed, such as tar, soot, coke and evolved gases resulting from devolatilization of the binder, binder coke and carbon aggregate during the preheating, baking and soaking steps must be collected and/0r `disposed of.

More specifically, the temperature within the kiln tunnel 10 must be progressively increased at predetermined and controlled rates from the left end or entrance to the preheating zone A towards the right end of the baking zone B, and thereafter maintained substantially constant over the length of the soaking zone C, while the tar resulting from devolatilization and distillation of the binder in preheating zone A, and the soot, coke and gaseous products resulting from devolatilization and coking of the binder coke and carbon aggregate generated principally in the baking zone B and soaking zone C, are collected `and `disposed of substantially simultaneously and sequentially with their generation. Finally, the temperature must be progressively decreased from left to right over the length of cooling zone D.

The several aforedescribed `essential temperature zones within the ware chamber 10 of the apparatus selected for purposes of illustrating the invention are acquired and maintained primarily by strict regulation and distribution of the hea-t supplied by the burners I4. Some additional heart is obtained in the soaking zone C by combustion of limi-ted amounts of soot, coke and gas generated within the kiln tunnel I0, the coke, for the most part, being deposited on the inside walls of the ware chamber in the soaking zone, land the soot entrained in the generated kiln gases.

The fuel input to the burners 14 is preferably controlled by means of commercially available temperature sensing devices located strategically in the crown or roof of the kiln tunnel l0, iirst, to develop and insure the maximum predetermined required uniform soaking temperature in zone C, and second, to produce and insure progressively decreasing temperatures from soaking zone C through baking zone B towardsthe preheating zone A.

On reference to FIG. l, it will be observed that the products of combustion from burners 1d flow from right to left in the muies l2 toward the exhaust stack there shown. By adjusting the fuel to the various burners, it is thus possible to generate and distribute heat along zones B and C, as desired.

The heat required in the preheating zone A is less intense than that required in zones B and C and `may be supplied in various ways. In one arrangement the heat and temperature conditions required in zone A may be obtained by circulating controlled mixtures of hot products of combustion from the muffles 12 and air through a series of tubes or conduits installed in zone A. By proper location of the tubes or conduits leading into zone A of the kiln, and through adjustment of the ratio and -total quantity of hot gas and air introduced through the aforesaid tubes or conduits, the desired rate of temperature rise and maximum predetermined preheating temperature are readily obtained in this zone.

Cooling of the carbon articles in zone D may be accomplished in various ways, such as by means of -a series of horizontal or vertical pipes or conduits disposed along the interior Walls and/or crown of the cooling zone of the kiln tunnel through which cool air or other coolant is drawn, or by introducing a cool non-oxidizing or inert gas into direct contact with the carbon articles through suitable openings in the crown of cooling zone D. By adjusting the amount of gas or coolant so introduced, the desired rates of cooling are obtainable.

Devolatilization of the binder in its conversion to coke produces loweraboiling volatiles mainly in the preheating zone A, and to a lesser -degree in the baking zone B. These lower-boiling volatiles are disposable in various ways in accordance with the practice of the invention. One manner of disposing of a portion of these lowerboiling volatiles and kiln gases resulting from them is by maintaining pressures within the left hand or exit portions of the combustion ues 12 at a value below the pressures obtaining in the Ware chamber 10 adjacent the left hand or exit portions of 4the combustion ues. Under these differential pressure conditions, volatile-containing kiln gases flow from the kiln tunnel or ware chamber 10 into ilues 12 through purposely spaced or porous brickwork of the interior wall separating the chamber 10 and ues 12, Where they are either burned in the flues 12 or disposed of through the exhaust stack in direct communication with the combustion flues 12. The greater the aforesaid pressure differential between the kiln tunnel 10 and fiues 12, adjacent the left hand end of the ues 12, the greater the gas flow from ware chamber 10 into the flues. Practice of the invention has revealed pressure ditferentials ranging from 0.001 to 0.5 inch of water to be satisfactory.

The aforesaid pressure differentials may be accomplished by creating suitable degrees of draft in the pipe -lines or ducts leading from ues 12 to their exhaust stack, as by the use of fans -and/ or dampers, or by inserting flow restrictions or dampers at suitable locations in the ues 12, as for example near the location where the baking zone B ends and soaking zone C begins.

A second portion of these lower-boiling volatiles ows linearly and axially along the interior of the kiln tunnel 10 into the cooler portions of the preheating zone A, where it condenses into liquid tar on the kiln Walls and floor. The door and walls of the kiln are preferably constructed to facilitate the ilow and collection of the tar condensate in a sump or sumps, below the floor of the preheating zone A, which may be provided with heating coils to maintain the tar in a fluid condition for removal therefrom at suitable intervals. Steam jacketed pumps have been employed to good advantage to empty the tar sumps.

A third portion of these lower-boiling volatiles ilows linearly and axially along the ware chamber 10 of the kiln into the hotter baking and soaking zones B and C, respectively, where it is cracked and produces gaseous products including hydrogen, as well as soot. Some of the resulting soot deposits on the carbon articles undergoing therrnal processing, and on the walls, crown and floor of the kiln; the remaining soot is suspended and iioats in the kiln gases.

`From the preceding description it will be evident that the gaseous atmosphere within the kiln tunnel 10 is in constant motion. As the temperature of the kiln gases rises, the flow pattern in preheating zone A, and in particular in the baking and soaking zones B and C, is in addition predominantly upwardly over the interior side Walls of the ware chamber 10, inwardly across and towards the center of the roof or crown of the kiln tunnel, and then medially downwardly into contact with the exposed surfaces of the carbon ware or products undergoing thermal processing within the kiln tunnel 10, this circulatory gas flow picking up and entraining volatiles emanating from the carbon articles, and then back upwardly along the hot side walls of the kiln.

Since the aromatic organic binders Vfound satisfactory in the practice of the invention generate substantial quantities of volatile hydrocarbons, as well as lesser amounts of other gaseous decomposition products, the circulation of the hydrocarbon-laden gases in 'baking Zone B and soaking zone C, as aforedescribed, causes at least a portion of the hydrocarbons to come in contact with the reltaively hot side walls in these two kiln zones. When this occurs, the gases are cracked into hydrogen or lighter hydrocarbons and coke, with the coke depositing on the interior walls of the kiln. Unless these coke deposits, which are of a very hard variety resembling pitch coke, are removed, they will grow inwardly into the kiln tunnel 10 and eventually obstruct and interfere with passage of the carbon articles under treatment through the kiln.

These coke deposits, much of the soot entrained in the kiln gases, and some of the kiln gases themselves may be disposed of in the practice of the invention by maintaining a condition of higher pressure in the lues 12 in those portions adjacent the kiln tunnel 10 where the coke deposits occur than the pressure existing within the kiln chamber 10 at substantially the same location. This pressure diierential condition causes gaseous products of combustion, containing carbon dioxide, water vapor and excess air, to ow from the flues 12 through the porous walls separating the tlues from the kiln tunnel 10 adjacent the coke deposits. The location and amount of the products of combustion so introduced are controllable by increasing or decreasing the pressure within the ues 12 relative to the pressure in the kiln tunnel 10.

When so introduced into the kiln ware chamber 10, these products of combustion first make contact with the coke deposited on the interior kiln walls and, at the operating temperatures in the baking and soaking zones, the coke deposits are consumed by combustion.

Passage of any additional gaseous products from the flues 12 into the kiln tunnel 10, greater than that required to consume the coke deposits, Will support combustion of the kiln-generated gases, including the aforementioned entrained soot. This latter condition signals the limit of yue gas infiltration into the chamber 10 that can be tolerated, since flue gases in excess of the amount required to burn or consume the deposited coke, entrained soot, and combustible kiln-generated gases would be available to support burning of the carbon articles under thermal processing in the kiln tunnel 10.

Gas infiltration through the porous walls of the mule flues 12 into the kiln ware chamber 10, in the areas therein where coke deposits occur, and the level of such infiltration, will depend on the ease at which the gas passes through the mufe walls and on the amount of deposited coke and entrained soot to be consumed. A pressure in the lues 12 of 0.001 to 0.5 inch of Water above that in vthe Ware chamber 1t) adjacent theareas of coke deposit has assured combustion or burning of substantially all of the coke deposits, considerable amounts of entrained soot and some of the combustile kiln-generated gases, without burning the `carbon articles under treatment.

Attainment of the desired pressure and oxidizing relationships Abetween the flues 12 and kiln chamber 10 adjacent the coke deposits therein can be accomplished by adjustment of dampers or valve mechanisms in the exhaust lines from flues 12 to the exhaust stack, adjustment -o external sources of pressurizing atmosphere and variation of secondary air introduced to the ues 12 adjacent the coke deposit areas in the kiln chamber l0, incorporation of restrictions or baffles within the lines 12 at desired locations along their length, or by combinations of any two or more of the enunciated means. As an alternative to any one or more of the above means for consuming the coke deposits and soot within the kiln tunnel lil, intermittently operated steam jets 31S may be employed for admitting steam in amount suflicient to support combustion of the coke and soot.

From the foregoing description of the operating pressure differentials between the combustion flues 12 and kiln tunnel 1t), it will be observed that positive pressure conditions are maintained in the right hand portion of flues 12 relative to the pressure within the kiln tunnel lll adjacent thereto, and negative pressure conditi-ons are maintained in the left hand portion of ilues l2 relative to the pressure within the kiln tunnel lil adjacent thereto. These are precisely the operating conditions required in the practice of the invention and they can be accomplished, as previously described.

In addition to the transverse circulating ilow pattern of the kiln gases upwardly, laterally inwardly and centrally downwardly and laterally outwardly within the kiln tunnel 10, as previously described, the kiln gases also tend to ow axially outwardly along the crown of the kiln from the highest temperature in Zone C both toward the baking and preheating Zones B and A, respectively, and toward the cooling zone D, then back from those zones towards Zone C in the lower portion of the kiln chamber lil.

Such axial circulatory flow of the kiln-generated gases is generally undesirable, especially over the length of cooling zone D, since it acts to drag or conduct heat into a zone where it is desired to extract or remove heat. It also serves to drag or convey soot from the heated zones of the kiln into the cooling area, zone D, where it may be deposited, not only on the carbon articles therein, but on the side walls7 crown and any cooling conduits or similar cooling devices, thereby reducing their eiiciency.

This longitudinal or axial flow pattern of the kilngenerated gases has been reduced, prevented, or even reversed by introducing substantially carbon-inert, nonreactive or non-oxidizing gases into the interior of the kiln tunnel l@ through the crown thereof at suitable locations along its length. Gases for this purpose have been obtained in at least three diierent ways.

In one Imethod of operation, hot gases are drawn of the kiln through the crown in the soaking zone C, passed through cleaning and cooling equipment to remove substantially all the entrained soot and to cool the gases, after which the gases are returned to the kiln through suitable inlets to zones A, B and D. Control of this recirculation may be obtained `by a variety of means such as power driven fan and adjustable dampers or valves.

ln a second method of operation, gases or products from an inert gas generator are charged into the kiln tunnel 1t) at the same locations referred to in the first method of operation.

A third way is to so operate the kiln that the products of combustion in the flu-es 12 are substantially inert and then circulate a portion thereof in a manner similar to the first two described methods.

:Other gases substantially non-reactive or non-oxidizing to the carbon products being treated, such as fuel gases, may if desired, be substituted in any of the three methods stated above. Regardless of the method employed, it is 4preferred to use a gas that is low in combustibles and containing not more than two percent by volume of oxygen. The amount of gas required to minimize or substantially if not totally eliminate longitudinal flow of the kiln-generated gases can be regulated by suitable commercial ilow meters. Amounts up to 200 cubic feet per minute have performed satisfactorily.

It should be understood that introduction of gases to reduce, eliminate, or even reverse the longitudinal axial ow of the hot kiln-generated gases can have in addition -an important influence on the distribution of temperature within the kiln tunnel lll. It is possible, for example, to introduce suiicient cool gas into the zone D at a plurality of locations along its length to supply the entire cooling requirements for the carbon articles therein. Furthermore, controlled introduction of cool gas into any portion of the kiln will reduce the temperature therein, and this procedure may be employed as an lalternative method for regulating the rate of temperature rise in preheating zone A.

T-he amount of cool gas introduced into the kiln tunnel 1t) in accordance with yany of the methods herein described is readily controlled by means of dampers which are opened or closed in response to commercially available control mechanisms actuated by any well known temperature sensing devices installed in the crown of the kiln near the locations where cool gas is to be introduced and required.

lin addition to gases required as just described for reducing, preventing or reversing the axial ilow of the gases within kiln tunnel 1t), or for assisting in controlling kiln temperatures, similar inert or non-reactive gases, obtained by recirculating cleaned and cooled kiln gases, or produced by an inert gas generator, or obtained from low-oxygen products of combustion, may be introduced under the train of cars Ztl to raise the pressure at this location, as well as being employed to purge the vestibules or lock chambers 15 at the ends of the kiln.

For example, referring to FIG. 1, each time a load of carbon articles is introduced into vestibule 15 at the left or entrance end to the kiln, the inner door 16 and the outer door 18 are closed, after which the atmospheric air in the vestibule is ushed out or purged by introducing any one or mixtures of the aforementioned inert gases until the oxygen content of the lgas in the vestibule is redu-ced below about two percent by volume. In this way explosions are avoided when door 16 is opened to permit admittance of the load into the kiln tunnel 10.

Similarly, at the exit or right hand end of the kiln, before the inner door 16 is opened to permit movement of a load into the discharge vestibule 15, the atmosphere in the vestibule is purged, with both doors 16 and 18 closed, until the oxygen content of the atmosphere has dropped below two percent by volume, as determined by analysis of gas samples taken at suitable intervals.

ln a practical `demonstration of Ithe progressive thermal processing method of the invention, pressed green carbon anode blocks 13 x 17" x 12" tall were fabricated from calcined petroleum coke having the following Tyler standard screen analysis- Percent aggregate Tyler screen mesh per lineal inch: retained on screen 200 13.7 Pan 29.4

in admixture with 18.5 percent -by weight coal-tar pitch binder, having a cube-in-air melting point of C. These green carbon anode blocks were stacked two-high in spaced parallel rows on the cars 20, without the use of granular packing material, saggers, or other supporting media, and the loaded cars were successively charged into a mufe-type kiln of the general type hereinabove described. Each loaded car was charged into the gas lock chamber l5 at the extreme left hand end of the kiln tunnel 10. The gas lock, with its doors 16 and 1:8 in gas-tight closed position was then purged of atmospheric contamination by recirculated kiln gases, or inert gas from a gas generator. Thereafter the door 16 was opened and the loaded car 20 advanced into the preheating zone A. Subsequently, at four-hour intervals, an additional carload of green carbon anode blocks was charged into the ware chamber of the kiln in the same manner.

Charging of the loaded cars into the kiln, as above described, physically and periodically advanced the carbon anode blocks successively and progressively through the preheating zone A, where their temperature was raised to approximately 550 C. at an approximate rate` of 10 C. per hour.

Continued charging of cars 20 loaded with green carbon anode blocks through the entrance lock chamber 15 into the preheating zone A physically and periodically advanced the anodes `from the preheating zone A into and through the baking zone B, where they were elevated in temperature to `apprcnrimately 1100 C. at a rate of about 40 C. per hour.

Following the baking treatment in zone B, the loaded cars were further advanced into the soaking zone C, Where the temperature of the carbon anodes was held at substantially the maximum temperature of l100 C. reached in the baking zone B for `a period of from 14 to 24 hours.

The nal cooling step or treatment was then accomplished by advancingy the cars and carbon anode blocks supported thereon into and through the cooling zone D, where the temperature of the anodes was progressively reduced to Tapproximately 275 C. in about 33 hours at an approximate rate of 25 C. per hour.

The baked carbon anodes were thereafter discharged from the cooling zone D of the kiln through the discharge gas lock chamber 15, the lock chamber having been purged in the same manner described for the inlet lock llS before opening its door 16 to receive each load of baked anodes from the interior of the kiln tunnel 10.

The atmosphere within the kiln tunnel 10 was maintained substantially inert to the carbon anodes therein during their entire progress through the kiln and the baked anodes discharged therefrom were sound, crack-free and undistorted in respect to their original green geometric shape. Anodes thus baked were employed successfully in an electrolytic reduction cell used in the commercial production of metallic aluminum.

The tars, soot, coke and gases distilled from the binder and carbon aggregate were substantially all disposed of substantially concurrently with their generation during the thermal processing herein described and in accordance with the practice of the invention heretofore described.

Although the invention has been described and illustrated in more or less specic terms, it will be apparent to personnel skilled in the art to which it appertains that changes may be made therein without departing from the spirit of the invention asserted in the appended claims.

What is claimed is:

1. A process for producing hard dense undistorted baked carbon articles from green carbon articles preshaped in self-supporting plastic condition from formulations comprising one or more comrninuted carbon aggregates selected from the group consisting of bituminous coal coke, anthracite coal, pitch coke and petroleum coke in admixture with 5 to 25 percent by weight of at least one aromatic organic binder characterized by yielding volatiles productive of tar, soot and coke residues at elevated temperatures and selected from the group consisting of oil-gas pitch, coke-oven pitch, lignite pitch, petroleum pitch and coal-tar pitch, by progressively moving the carbon articles laterally unsupported through an enclosing zone providing temperature-controlled preheating, baking, soaking and cooling Zones in successive intercommunication, the steps comprising providing a substantially inert atmosphere within the enclosing zone at a pressure above atmospheric, preheating the carbon articles to ya temperature between 400 and 600 C. at a rate of 2 to 40 C. per hour to ydevolatilize the binder, convert it to coke and release lower-boiling fractions volatilizable during preheating, condensing lower-boiling tar-producing fractions and collecting the tar so produced substantially concurrently with the preheating step, advancing the preheated carbon articles through a progressively rising temperature zone and Ibaking the carbon articles at a temperature between 800 and l300 C` -at a rate of 4 to 50 C. per hour, further advancing the preheated and baked carbon articles into a constant temperature soaking zone held at substantially the maximum temperature reached during baking for a period of l to 2O hours, said baking and soaking treatments devolatilizing and releasing the higherboiling coke-forming, soot-forming and :gaseous fractions of the binder coke and carbon aggregate constituents of the carbon articles, supplying combustion supporting gaseous media in admixt-ure with the released higher-boiling fractions in amount suiicient to consume coke and soot residues formed therefrom, while maintaining an inert environment in contact with the exposed surface areas of the car-bon articles, and thereafter advancing the preheated, baked and soaked carbon articles into and through a pro-gressively reduced temperature cooling zone to lower the temperature of the carbon articles to between 200 and 400 C. at a rate of 2 to 507 C. per hour.

2. In thermal processing of self-supporting green carbon articles preformed from admixtures of comminuted carbon aggregate and an aromatic organic binder, the binder having a cube-in-air melting point between C. and C., being present in amounts between 5 and 25 percent by weight of the tadmixtures and characterized by yielding volatiles productive of tar, soot and coke residues at elevated temperatures, by progressively moving the carbon articles laterally-unsupported through an enclosing zone providing temperature-controlled successively arranged intercommunicating preheating, baking, soaking and cooling zones, the steps comprising supplying a substantially inert atmosphere within the enclosing zone at a pressure above atmospheric, preheating the preformed carbon articles at a predetermined rate of temperature rise to a predetermined maximum temperature between 400 and 50V C. at which temperature the organic binder is substantially devolatilized and converted to coke and the carbon articles take on a substantially permanent set, condensing a portion of the tar-producing volatiles released from the binder during the preheating step and removing the tar so produced from the preheating zone, elevating the temperature of the preheated carbon articles in the baking Zone to a predetermined temperature between 800 and 1300" C. over a suiicient period of time to substantially Idevolatilize the binder coke and carbon aggregate and increase the density of the car-bon articles above their density in the preheated condition, soaking the preheated and baked carbon articles at substantially the maximum temperature reached during baking for a suiiicient time to further densify and remove residual stresses in the carbon articles in the soaking zone, and progressively cooling the preheated, baked and soaked carbon articles in the cooling zone to a predetermined temperature suiiciently low to avoid their burning or discharge from the cooling zone to atmosphere.

3. In thermal processing of self-supporting green carbon articles preformed from admixtures of comminuted carbon aggregate and an aromatic organic binder, characterized by yielding tar-producing volatiles at elevated temperatures, by progressively moving the carbon articles through successively 'arranged intercommunicating and enclosing preheating, baking, soaking and cooling zones in the absence of intermediate cooling and article-packing media in contact with the carbon articles, the steps comprising supplying an inert atmosphere above atmospheric pressure within the enclosing zones, preheating the preformed carbon articles yat a predetermined rate of temperature rise to a predetermined maximum temperature during which preheating treatment the binder is substantially devolatilized and converted to coke and the carbon articles assume a substantially permanent set, condensing lower-boiling voltatilized tar-producing components of the binder substantially concurrently with their generation 13 during preheating and collecting the tar so produced, raising the temperature of the carbon articles above the predetermined maximum preheating temperature to an elevated predetermined maximum baking temperature between 800 and 1300" C. over a sufcient period of time to substantially devolatilize the binder coke and carbon aggregate and increase the density of the carbon articles, soaking the preheated and baked carbon -articles at substantially the maximum temperature reached during baking for a sutlicient time to substantially complete devolatilization of the binder coke and carbon aggregate and thereby further increase the density of the carbon articles and remove residual strains therein, burning gaseous products resulting from the devolatilization of the binder coke and carbon aggregate during the baking and soaking steps, and progressively cooling the preheated, baked and soaked carbon articles to a predetermined temperature sufficiently low to avoid their burning on discharge from the cooling zone to atmosphere.

4. In thermal processing of self-supporting green carbon articles from formulations of one or more comminuted carbon aggregates selected from the group consist-ing of anthracite coal, bituminous coal coke, pitch coke, and petroleum coke in admixture with at least one of the aromatic organic binders selected from the group consisting of oil-gas pitch, coke-oven pitch, lignite pitch, petroleum pitch and coal-tar pitch, said binder being characterized by yielding lower-boiling tar-producing volatiles at elevated temperatures, the steps comprising providing enclosing preheating, baking, soaking and cooling zones in successive intercommunicating arrangement, supplying -an inert atmosphere above atmospheric pressure within the enclosing zones, preheating the preformed carbon articles at a predetermined rate of temperature rise to a predetermined maximum temperature during which preheating treatment the binder is substantially devolatilized and converted to coke and the carbon articles assume a substantially permanent set, condensing lower-boiling volatilized tar-producing components of the binder substantially concurrently with their generation during preheating and collecting the tar so produced, raising the temperature of the carbon articles above the predetermined maximum preheating temperature to an elevated predetermined maximum baking temperature between 800 and 1300 C. over a suicient period of time to substantially idevolatilize the binder coke and carbon aggregate and increase the density of the carbon articles, soaking the preheated and baked carbon articles at substantially the maxirnum temperature reached during baking for a suiiicient time to substantially complete devolatilization of the binder coke and carbon aggregate and thereby further increase the density of the carbon articles and remove residual strains therein, burning higher-boiling fractions resulting from the devolatilization of the binder coke and carbon aggregate during the baking and soaking steps, and progressively cooling the preheated, baked and soaked carbon articles to a predetermined temperature sufciently low to avoid their burning on discharge from the cooling zone to atmosphere.

5. In thermal processing ot' self-supporting green carbon articles preformed from formulations of at least one carbon aggregate selected from the group consisting of bituminous co-al coke, anthracite coal, pitch coke and petroleum coke comminuted and falling within the following Tyler standard screen analyses- Percent aggregate retained on screen Tyler screen mesh per lineal inch:

in admixture with at least one aromatic organic binder having a cube-in-air melting point of between C. and C. and present in amounts between 12 and 20 percent by weight of the formulations, said binder being characterized by yielding tar-producing lower-boiling volatiles at elevated temperatures, the steps comprising providing a closed system of preheating, baking, soaking and cooling zones in successive communication enclosing and maintaining an environment inert to the carbon articles at a pressure above atmospheric, periodically charging the preformed green carbon articles in the absence of surface-contacting packing media into the preheating zone and raising the temperature of the carbon articles therein `at the rate of 2 to 40 C. per hour to a predetermined maximum temperature between 400 and 600 C., condensing a portion of the tar-producing volatiles released from the binder during the preheating step and removing the tar so produced from the preheating zone, advancing the preheated carbon articles into the baking Zone and further elevating the temperature of the carbon articles to a predetermined maximum temperature between 800 and 1300 C. at a rate of 4 to 50 C. per hour, advancing the carbon articles into the soaking zone and holding the temperature of the preheated and baked carbon articles at substantially the maximum temperature reached during baking for a period of 1 to 20 hours, thereafter advancing the preheated, baked and soaked carbon articles into the cooling zone and progressively lowering the temperature of the carbon `articles to between 200 and 400 C. at a rate of 2 to 50 C. per hour, and combustibly consuming higher-boiling fractions and products of carboniz-ation resulting from volatilization of the binder and carbon aggregate components of the carbon articles within the closed zoned system.

6. In a thermal processing method of treating selfsupporting preformed green carbon `articles to produce baked carbon products therefrom of substantially the geometric shape of the preformed green carbon articles initially made from admixtures of comminuted carbon aggregate and an organic carbonaceous binder yielding volatiles productive of tar, soot and coke residues at elevated temperatures, the steps comprising, charging and progressively advancing the preformed green carbon articles in laterally-unsupported condition through an enclosing zone providing temperature-controlled preheating, baking, soaking and cooling zones in successive intercommunication, supplying a substantially inert atmosphere W-ithin the enclosing zone at pressures above atmospheric, preheating the carbon articles in the preheating zone over a gradiently rising temperature range to a maximum predetermined temperature at which the organic carbonaceous binder is substantially devolatilized, releases tar-producing lower-boiling 'volatiles and is substantially completely yconverted to coke, establishing rearward flow of a portion of the volatiles so released towards the low temperature end of the preheating zone where they condense and are removed from the preheating zone in the form of tar, advancing the preheated carbon articles into the baking zone and raising their temperature therein `above the maximum temperature reached in the preheating zone to a predetermined temperature at which the formed binder coke and carbon aggregate components of the preheated carbon articles are substantially devolatilized and at least a portion of the released volatiles are cracked and converted to soot and coke in the baking zone, delivering the preheated and baked carbon articles at substantially the maximum temperature reached during baking into the soaking zone and holding the same at substantially the maximum temperature reached during baking for `a suicient time to density and remove residual stresses in the carbon articles, and advancing the preheated, baked and soaked carbon articles into the cooling zone to progressively cool the same from their soaking temperature to a predeterl mined temperature suiiiciently low to avoid their burning on discharge from the cooling zone to atmosphere.

7. In a thermal processing method of treating selfsupporting preformed green carbon articles to produce baked carbon products therefrom of substantially the geometric shape of the preformed green carbon articles initially made from admixtures of comminuted carbon aggregate and an organic carbonaceous binder yielding volatiles productive of t-ar, soot and coke residues at elevated temperatures, the steps comprising, charging and progressively advancing the preformed green carbon articles in laterally-unsupported condition through an enclosing zone providing temperature-controlled preheating, baking, soaking and cooling Zones in succsive intercommunication, supplying .a substantially inert atmosphere within the enclosing zone at pressures above atmospheric, preheating the carbon articles in the preheating zone over a gradiently rising temperature range to a maximum predetermined temperature at which the oirganic carbonaceous binder is substantially devola tilized, releases tar-producing lower-boiling volatiles and is substantially completely converted to coke, establishing rearward flow of a portion of the volatiles so released towards the low temperature end of the preheating zone where they condense and are removed from the preheating zone in the form of tar, establishing yforward ow of another portion of the volatiles so released into the baking zone and advancing the preheated carbon articles thereinto and raising their temperature therein above the maximum temperature reached in the preheating zone to a predetermined temperature at which the formed binder coke and carbon aggregate components of the preheated carbon articles are substantially devolatilized and at least a portion of their released volatiles and forwardly advanced volatiles therein are cracked and converted to soot and coke residues, exhausting soot residues from and combustibly consuming coke residues within the baking Zone, delivering the preheated and baked carbon articles at substantially the maximum temperature reached during bak-ing into the soaking zone and holding the same :at substantially the maximum temperature reached during baking for a suioient time to densify and remove residual stresses in the carbon articles, and advancing the preheated, baked and soaked carbon articles into the cooling zone to progressively cool the same from their soaking temperature to a predetermined temperature sufciently low to avoid their burning on `discharge from the cooling zone to atmosphere.

8. In a thermal processing method of treating selfsupporting preformed green carbon articles to produce baked carbon products therefrom of substantially the geometric shape of the preformed green carbon articles initially made from admixtures of cornminuted carbon aggregate and an onganic carbonaceous binder yielding volatiles productive of tar, soot and coke residues at elevated temperatures, the steps comprising, charging and progressively advancing the preformed green carbon articles in laterally-unsupported condition through an enclosing zone providing temperature-controlled preheating, baking, soaking and cooling zones in successive intercommunication, supplying a substantially inert atmosphere within the enclosing zone at pressures above atmospheric, preheating the carbon articles in the preheating zone over a gradiently rising temperature range to a maximum predetermined temperature at which the organic carbonaceous binder is substantially devolatilized, releases tar-producing lower-boiling volatiles, is substantially completely converted to coke, and the carbon articles take on a substantially permanent set, establishing rearward flow of a portion of the volatiles so released towards the low temperature end of the preheating zone where they condense and are removed from the preheating zone in the form of tar, establishing forward flow of another portion of the volatiles so released into the baking zone and advancing the preheated carbon articles thereinto and raising their temperature gradiently therein above the maximum temperature reached in the preheating Zone to a predetermined maximum temperature at which the formed binder coke and carbon laggregate components of the preheated carbon articles are substantially devolatilized and at least a portion of their released volatiles and forwardly advanced volatiles are cracked and converted to soot and coke residues in the baking Zone, combustibly consuming coke residues inthe baking zone, delivering the preheated and baked carbon articles at substantially the maximum temperature reached during baking into the soaking zone and holding the same at substantially the maximum temperature reached during baking for a suiiicient time to densify and remove residual stresses in the carbon articles, and advancing the preheated, baked and soaked carbon articles into the cooling Zone to progressively cool the same from their soaking temperature to la predetermined temperature suciently low to avoid their burning on discharge from the cooling zone to atmosphere.

9. In a thermal processing method of treating selfsupporting preformed green carbon articles lto produce baked carbon products therefrom of substantially the geometric shape of the preformed green carbon articles initially made from admixtures of at least one comminuted carbon aggregate selected from the .group consisting of anthracite coal, bituminous coal coke, pitch coke and petroleum coke, jat least one organic carbonaceous binder selected from the group consisting of oilgas pitch, coke-oven pitch, lignite pitch, petroleum pitch and coal-tar pitch and yielding volatiles productive of tar, soot and coke residues at elevated temperatures, the steps comprising, charging and progressively advancing the preformed green carbon articles in laterally-unsupported condition through an enclosing zone providing temperature-controlled preheating, baking, soaking and cooling Zones in successive intercommunication, supplying a substantially inert atmosphere within .the enclosing zone at pressures above atmospheric, providing a combustible gas-fired muifle heating zone exterior to and substantially contiguous with the baking and soaking zones, supplying indirect heat to the preheating, baking and soaking zones from heat generated within the muftle heating Zone preheating the carbon articles in the preheating zone over a gradiently rising temperature range to a maximum predetermined temperature at which the organic carbonaceous binder is substantially devolatilized, releases tar-producing lower-boiling volatiles, is substantially completely converted to coke, and the carbon articles take on a substantially permanent set, establishing rearward ilow of a portion of the volatiles so released towards the low temperature end of the preheating zone where they condense and are .removed from the preheating zone in the form of tar, advancing the preheated carbon articles into the baking zone and raising their temperature gradiently therein above the maximum ternperature reached in the preheating zone to a predetermined maximum temperature at which the formed binder coke and carbon aggregate components of the preheated carbon articles are substantially devolatilized and at least a portion of the released volatiles are cracked and converted to soot and coke in the baking zone, delivering the preheated and baked carbon articles at substantially the maximum temperature reached during baking into the soaking zone and holding the same at substantially the maximum temperature reached during baking for a sufiicient time to density and remove residual stresses in the carbon articles, and advancing the preheated, baked and soaked carbon articles into the cooling zone to progressively cool the same from their soaking temperature to a predetermined temperature suiiiciently low to avoid their burning on discharge from the cooling zone to atmosphere.

10. In a thermal processing method of treating selfsupponting preformed green carbon articles to produce baked carbon products therefrom of `substantially the geometric shape of the preformed green carbon articles initially made from admixtures of comminuted carbon aggregate and an organic carbonaceous binder having a cube-in-air melting point between 75 C. and 150 C and yielding volatiles productive of tar, soot and coke residues at elevated temperatures, the steps comprising, charging and progressively advancing the preformed green carbon articles in laterally-unsupported condition through an enclosing Zone providing temperature-controlled preheating, baking, soaking and cooling Zones in successive intercommunication, supplying a substantially inert atmosphere within the enclosing zone at pressures above atmospheric, providing a combustible gas-tired mufe heating Zone exterior to and substantially contiguous with the baking and soaking zones, supplying indirect heat to the preheating, baking and soaking zones from heat generated within the mufe heating Zone, preheating the carbon articles in the preheating zone over a gradiently rising temperature range to a maximum predetermined temperature at which the organic carbonaceous binder is substantially devolatilized, releases tar-producing lower-boiling volatiles, is substantiallycompletely converted to coke, and the carbon articles take on a substantially permanent set, establishing rearward llow of a portion of the volatiles so released towards the low temperature end of the preheating Zone where they condense and are removed from the preheating zone in the form of tar, advancing the preheated carbon articles into the baking Zone and raising their temperature gradiently therein above the maximum temperature reached in the preheating zone to a predetermined maximum temperature at which the formed binder coke and carbon aggregate components of the preheated carbo-n articles are substantially devolatilized and at least a portion of the released volatiles are cracked and converted to soot and coke in the baking Zone, delivering the preheated and baked carbon articles at substantially the maximum temperature reached during baking into the soaking zone and holding the same at substantially the maximum temperature reached during baking for a sutlcient time to density and remove residual stresses in the carbon articles, and advancing the preheated, baked and soaked carbon articles into the cooling zone to progressively cool the same from their soaking temperature to a predetermined temperature sufciently low to avoid their burning on discharge from the cooling zone to atmosphere.

ll. In a thermal processing method of treating selfsupporting preformed green carbon articles to produce baked carbon products therefrom of substantially the geometric shape of the preformed green carbon articles initially made from admixtures of at least one comminuted carbon aggregate selected from the group consisting of anthracite coal, bituminous coal coke, pitch coke and petroleum coke, and at least one organic carbonaceous binder selected from the group consisting of oil-gas pitch, coke-oven pitch, lignite pitch, petroleum pitch and coaltar pitch, having a cube-in-air melting poin-t between 75 C. and 150 C. and yielding volatiles productive of tar, soot and coke residues at elevated temperatures, the steps comprising, charging and progressively advancing the preformed green carbon articles in laterally-unsupported condition through an enclosing zone providing temperature-controlled preheating, baking, soaking and cooling zones in successive intercommunication, supplying a substantially inert atmosphere within the enclosing Zone at pressures above atmospheric, providing a cornbustible gas-tired inutile heating Zone exterior to and substantially contiguous with the baking and soaking zones, supplying heat to the preheating, baking and soaking zones from heat generated within the mule heating zone, preheating the carbon articles in the preheating zone over a gradiently rising temperature range to a maximum predetermined temperature at which the organic carbonaceous binder is substantially devolatilized, releases tar- 18 producing lower-boiling volatiles. is substantiallv completely converted to coke, and the carbon articles take on a substantially permanent set, establishing rearward flow of a portion of the volatiles so released towards the low temperature end of the preheating zone where they condense and are removed from the preheating zone in the form of tar, establishing forward flow of another portion of the volatiles so released into the baking zone and advancing the preheated carbon articles thereinto and raising their temperature gradiently therein above the maximum temperature reached in the preheating zone to a predetermined maximum temperature at which the formed binder coke and carbon aggregate components of the preheated carbon articles are substantially devolatilized and at least a portion of the released volatiles and forwardly advanced volatiles are cracked and converted to soot and coke residues in the baking Zone, delivering the preheated and baked lcarbon articles at substantially the maximum temperature reached during baking into the soaking zone and holding the same at substantially the maximum temperature reached during baking for a sufficient time to densify and remove residual stresses in the carbon articles, withdrawing soot residues into the mule heating zone, and advancing the preheated, baked and soaked carbon articles into the cooling zone to progressively cool the same from their soaking temperature to a predetermined temperature sutlciently low to avoid their burning on discharge from the cooling Zone to atmosphere.

l2. In a thermal processing method of treating selfsupporting preformed green carbon articles to produce baked carbon products therefrom of substantially the geometric shape of the preformed green carbon articles initially made from admixtures of at least one comminuted carbon aggregate selected from the group consisting of anthracite coal, bituminous coal coke, pitch coke and petroleum coke, and at least one organic carbonaceous binder selected from the group consisting of oil-gas pitch, coke-oven pitch, lignite pitch, petroleum pitch and coaltar pitch, having a cube-in-air melting point between 75 C. and C. and yielding volatiles productive of tar, soot and coke residues lat elevated temperatures, the steps comprising, charging and progressively advancing the preformed green carbon articles in laterally-unsupported condition through an enclosing zone providing temperaturecontrolled preheating, baking, soaking and cooling zones in successive intercommunication, supplying a subst-antially inert atmosphere within the enclosing zone at pressures above atmospheric, providing a combustib-le gasred muiiie heating zone exterior to and substantially contiguous with the baking and soaking zones, supplying heat to the preheating, baking and soaking zones from heat generated within the mue heating zone, preheating the carbon articles in the preheating zone over a gradiently rising temperature range to a maximum predetermined temperature between 400 and 600 C. at which the organic carbonaceous binder is substantially devolatilized, releases tar-producing lower-boiling volatiles, is substantially completely converted to coke, and the carbon articles take on a substantially permanent set, establishing rearward flow of a portion of the volatiles so released towards t-he low temper-ature end of the preheating zone where they condense and are removed from the preheating zone in the form of tar, advancing the preheated carbon articles into the baking zone and raising their temperature gradiently therein above the maximum temperature reached in the preheating zone to a predetermined maximum temperature between 800 and 1300 C. at which the formed binder coke and carbon aggregate components of the preheated carbon articles are substantially devolatilized and at least a portion of the released volatiles are cracked and converted to soot and coke in the baking zone, delivering the preheated and baked carbon articles at substantially the maximum temperature reached during baking into the soaking zone and holding the same at substantially the maximum temperature reached during baking for a sucient time to densify and remove residual stresses in the carbon articles, and advancing the preheated, baked and soaked carbon articles into the cooling zone to progressively cool the same from their soaking temperature to a predetermined temperature sutciently low to avoid their burning on discharge from the cooling zone to atmosphere.

13. 'In a thermal processing method of treating selfsupporting preformed green carbon articles to produce hard dense undistorted baked carbon products therefrom of substantially the geometric shape of the preformed green carbon articles initially made from admixtures of at least one comminuted carbon aggregate selected from the group consisting of anthracite coal, bituminous coal coke, pitch coke and petroleum coke, and atleast one organic carbonaceous binder selected from the group consisting of oil-gas pitch, coke-oven pitch, lignite pitch, petroleum pitch and coal-tar pitch, having a cube-in-air melting point between 75 C. and 150 C. and yielding volatiles productive of tar, soot and coke residues at elevated temperatures, the steps comprising, charging and progressively advancing the preformed green car bon articles in laterally-unsupported condition through an enclosing zone providing temperature-controlled preheating, baking, soaking and cooling zones in successive intercommunication, supplying a substantially inert `atmosphere within the enclosing zone at pressures above atmospheric, preheating the carbon articles in the preheating zone over a gradiently rising temperature range at the rate of 2 to 40 C. per hour to a maximum predetermined temperature between 400 Iand 600 C. at which the organic carbonaceous binder is substantially devolatilized, releases tar-producing lower-boiling volatiles and is substantially completely converted to coke, establishing rearward flow of a portion of the volatiles so released towards the low temperature end of the preheating zone where they condense and are removed from the preheating zone in the form of tar, Iadvancing the preheated carbon articles into the baking zone and raising their temperature gradiently therein above the maximum temperature reached in the preheating zone at a rate of 4 to 50 C. per hour to a predetermined maximum temperature between 800 and 1300" C. at which the formed binder coke and carbon aggregate components of the preheated carbon articles are substantially devolatilized and at least a portion of the released volatiles are cracked and converted to soot and coke in the baking Zone, delivering the preheated and baked carbon articles at substantially the maximum temperature reached during -baking into the soaking zone land holding the same `at substantially the maximum temperature reached during baking for a time interval of 1 to 20 hours to density and remove residual stresses in the carbon articles, and advancing the preheated, baked and soaked carbon articles into the cooling zone and progressively cooling the same at a rate of 2 to 50 C. per hour from their soaking temperature to a predetermined temperature between 200 and 400 C. to avoid their burning on discharge from the cooling zone to atmosphere.

References Cited in the file of this patent UNITED STATES PATENTS 1,509,196 Dressler Sept. 23, f1924 1,549,867 Graveman Aug. 18, 1925 1,586,306 Grandal et al. May 25, 1926 2,062,370 Miller Dec. I, 1936 2,270,199 Thrune Ian. 13, 1942 2,653,878 Sejersted et al. Sept. 29, 1953 UNITED STATES PATENT. oFFIcE CERTIFICATE OF CORRECTION Patent No. 3,009863 v November 21gv 1(21 John S., Angevine It is Vhereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column lu line 43 for "orekssl:v read f"- aforesad eg line 44V for "'employmellt.I read employing m;- column 4d line 3l, for "descrpton read description n; column 5a line 2l for "'siutable" read suitable column 8 line 66T, for "comloustilel read combustible 4; column l2,I line 56Y for "or" read on u.

Signed and sealed this lOth day of April 1962.,

(SEAL) Attest:

ERNEST W. SWDER DAVID L. LADD Attesting Officer Commissioner of Paten 

6. IN A THERMAL PROCESSING METHOD OF TREATING SELFSUPPORTING PREFORMED GREEN CARBON ARTICLES TO PRODUCE BAKED CARBON PRODUCTS THEREFROM OF SUBSTANTIALLY THE GEOMETRIC SHAPE OF THE PREFORMED GREEN CARBON ARTICLES INITIALLY MADE FROM ADMIXTURES OF COMMINUTED CARBON AGGREGATE AND AN ORGANIC CARBONACEOUS BINDER YIELDING VOLATILES PRODUCTIVE OF TAR, SOOT AND COKE RESIDUES AT ELEVATED TEMPERATURES, THE STEPS COMPRISING, CHARGING AND PROGRESSIVELY ADVANCING THE PREFORMED GREEN CARBON ARTICLES IN LATERALLY-UNSUPPORTED CONDITION THROUGH AN ENCLOSING ZONE PROVIDING TEMPERATURE-CONTROLLED PREHEATING, BAKING, SOAKING AND COOLING ZONES IN SUCCESSIVE INTERCOMMUNICATION, SUPPLYING A SUBSTANTIALLY INERT ATMOSPHERE WITHIN THE ENCLOSING ZONE AT PRESSURES ABOVE ATMOSPHERIC, PREHEATING THE CARBON ARTICLES IN THE PREHEATING ZONE OVER A GRADIENTLY RISING TEMPERATURE RANGE TO A MAXIMUM PREDETERMINED TEMPERATURE AT WHICH THE ORGANIC CARBONACEOUS BINDER IS SUBSTANTIALLY DEVOLATILIZED, RELEASES TAR-PRODUCING LOWER-BOILING VOLATILES AND IS SUBSTANTIALLY COMPLETELY CONVERTED TO COKE, ESTABLISHING REARWARD FLOW OF A PORTION OF THE VOLATILES SO RELEASED TOWARDS THE LOW TEMPERATURE END OF THE PREHEATING ZONE WHERE THEY CONDENSE AND ARE REMOVED FROM THE PREHEATING ZONE IN THE FORM OF TAR, ADVANCING THE PREHEATED CARBON ARTICLES INTO THE BAKING ZONE AND RAISING THEIR TEMPERATURE THEREIN ABPVE THE MAXIMUM TEMPERATURE REACHED IN THE PREHEATING ZONE TO A PREDETERMINED TEMPERATURE AT WHICH THE FORMED BINDER COKE AND CARBON AGGREGATE COMPONENTS OF THE PREHEATED CARBON ARTICLES ARE SUBSTANTIALLY DEVOLATILIZED AND AT LEAST A PORTION OF THE RELEASED VOLATILES ARE CRACKED AND CONVERTED TO SOOT AND COKE IN THE BAKING ZONE, DELIVERING THE PREHEATED AND BAKED CARBON ARTICLES AT SUBSTANTIALLY THE MAXIMUM TEMPERATURE REACHED DURING BAKING INTO THE SOAKING ZONE AND HOLDING THE SAME AT SUBSTANTIALLY THE MAXIMUM TEMPERATURE REACHED DURING BAKING FOR A SUFFICIENT TIME TO DENSIFY AND REMOVE RESIDUAL STRESSES IN THE CARBON ARTICLES, AND ADVANCING THE PREHEATED, BAKED AND SOAKED CARBON ARTICLES INTO THE COOLING ZONE TO PROGRESSIVELY COOL THE SAME FROM THEIR SOAKING TEMPERATURE TO A PREDETERMINED TEMPERATURE SUFFICIENTLY LOW TO AVOID THEIR BURNING ON DISCHARGE FROM THE COOLING ZONE TO ATMOSPHERE. 